Staff turn once assembled outside hotel (9)
I believe the answer is:
truncheon
'staff' is the definition.
(I've seen this before)
'turn once assembled outside hotel' is the wordplay.
'assembled' indicates an anagram.
'outside' means one lot of letters goes inside another.
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'turn'+'once'='turnonce'
'turnonce' anagrammed gives 'trunceon'.
'trunceon' going around 'h' is 'TRUNCHEON'.
(Other definitions for truncheon that I've seen before include "Policeman's traditional weapon" , "Peelers' baton" , "Police staff" , "Policeman's club" , "Police baton" .)